Anders Ekbom

Therearemanygoodepidemiologytextbooksonthemarket,butmostoftheseare addressedtostudentsofpublichealthorpeoplewhodoclinicalresearchwithe- demiologicmethods. Thereisaneedforashortintroductiononhowepidemiologic methodsareusedinpublichealth,geneticandclinicalepidemiology,becausehealth professionalsneedtoknowbasicepidemiologicmethodscoveringetiologicaswell asprognosticfactorsofdiseases. Theyneedtoknowmoreaboutmethodologythan introductorytextsonpublichealthhavetooffer. Insomehealthfaculties,epidemiologyisnotevenpartoftheteachingcurri- lum. Webelievethistobeaseriousmistake. Medicalstudentsarestudentsofall aspectsofdiseasesandhealth. Withoutknowingsomethingaboutepidemiologythe cliniciansandotherhealthprofessionalscannotreadagrowingpartofthesci- ti cliteratureinanyreasonablycriticalwayandcannotnavigateintheworldof "evidence-basedmedicineandevidence-basedprevention. "Withoutskillsine- demiologicmethodologytheyareinthehandsofexpertsthatmaynotonlyhavean interestinhealth. Some health professionals may believe that only common sense is needed to conductepidemiologicalstudies,butthescienti cliteratureandthepublicdebate onhealthissuesindicatethatcommonsenseisofteninshortsupplyandmaynot thrivewithoutsomeformaltraining. Epidemiologic methods play a key role in identifying environmental, social, and genetic determinants of diseases. Clinical epidemiology addresses the tr- sitionfromdiseasetohealthortowardmortalityorsocialormedicalhandicaps. Publichealthepidemiologyaddressesthetransitionfrombeinghealthytobeingnot healthy. Descriptiveepidemiologyprovidesthediseasepatternthatisneededtolook athealthinabroadperspectiveandtosettheprioritiesright. Epidemiologyisabasic scienceofmedicinewhichaddresseskeyquestionssuchas"Whobecomesill?"and "Whatareimportantprognosticfactors?" Answerstosuchquestionsprovidethe basisforbetterpreventionandtreatmentofdiseases. Many people contributed to the writing of this book: medical students in Denmark,studentsofepidemiologyattheIEAEEPEsummercourseinFlorence, Italy,andstudentsofpublichealthinLosAngeles. Withouttechnicalassistance v vi Preface fromGitteNielsen,JenadeShelley,NinaHoheandPamMasangkaythebookwould neverhavematerialized. LosAngeles,California JornOlsen Odense,Denmark KaareChristensen IowaCity,Iowa JeffMurray Stockholm,Sweden AndersEkbom Contents Part I Descriptive Epidemiology 1 Measures of Disease Occurrence ...3 IncidenceandPrevalence ...4 Incidence...6 RatesandDynamicPopulations ...7 CalculatingObservationTime...9 Prevalence,Incidence,Duration ...10 MortalityandLifeExpectancy ...11 LifeExpectancy ...12 References...13 2 Estimates of Associations ...15 3 Age Standardization...19 4 Causes of Diseases ...23 References...28 5 Descriptive Epidemiology in Public Health...29 GraphicalModelsofCausalLinks ...33 References...35 6 Descriptive Epidemiology in Genetic Epidemiology...37 OccurrenceDatainGeneticEpidemiology ...37 ClusteringofTraitsandDiseasesinFamilies ...38 TheOccurrenceofGeneticDiseases ...40 References...41 7 Descriptive Epidemiology in Clinical Epidemiology...43 SuddenInfantDeathSyndrome(SIDS)...44 CytologicalScreeningforCervixCancer ...45 ChangesinTreatmentofJuvenileDiabetes ...46 References...47 vii viii Contents Part II Analytical Epidemiology 8 Design Options...51 CommonDesignsUsedtoEstimateAssociations...51 EcologicalStudy ...52 Case-ControlStudy...54 CohortStudy ...5 5 ExperimentalStudy ...56 Reference ...57 9 Follow-Up Studies ...59 TheNon-experimentalFollow-Up(Cohort)Study ...59 StudyingRiskasaFunctionofBMI ...60 LongitudinalExposureData...62 DifferentTypesofCohortorFollow-UpStudies...63 10 Case-Control Studies...67 Case-CohortSampling ...69 DensitySamplingofControls...69 Case-Non-caseStudy...71 PatientControls ...72 SecondaryIdenti cationoftheSourcePopulation ...74 Case-ControlStudiesUsingPrevalentCases...74 WhentoDoaCase-ControlStudy? ...77 References...78 11 The Cross-Sectional Study...79 12 The Randomized Controlled Trial (RCT) ...81 Reference ...

Therearemanygoodepidemiologytextbooksonthemarket,butmostoftheseare addressedtostudentsofpublichealthorpeoplewhodoclinicalresearchwithe- demiologicmethods. Thereisaneedforashortintroductiononhowepidemiologic methodsareusedinpublichealth,geneticandclinicalepidemiology,becausehealth professionalsneedtoknowbasicepidemiologicmethodscoveringetiologicaswell asprognosticfactorsofdiseases. Theyneedtoknowmoreaboutmethodologythan introductorytextsonpublichealthhavetooffer. Insomehealthfaculties,epidemiologyisnotevenpartoftheteachingcurri- lum. Webelievethistobeaseriousmistake. Medicalstudentsarestudentsofall aspectsofdiseasesandhealth. Withoutknowingsomethingaboutepidemiologythe cliniciansandotherhealthprofessionalscannotreadagrowingpartofthesci- ti cliteratureinanyreasonablycriticalwayandcannotnavigateintheworldof "evidence-basedmedicineandevidence-basedprevention. "Withoutskillsine- demiologicmethodologytheyareinthehandsofexpertsthatmaynotonlyhavean interestinhealth. Some health professionals may believe that only common sense is needed to conductepidemiologicalstudies,butthescienti cliteratureandthepublicdebate onhealthissuesindicatethatcommonsenseisofteninshortsupplyandmaynot thrivewithoutsomeformaltraining. Epidemiologic methods play a key role in identifying environmental, social, and genetic determinants of diseases. Clinical epidemiology addresses the tr- sitionfromdiseasetohealthortowardmortalityorsocialormedicalhandicaps. Publichealthepidemiologyaddressesthetransitionfrombeinghealthytobeingnot healthy. Descriptiveepidemiologyprovidesthediseasepatternthatisneededtolook athealthinabroadperspectiveandtosettheprioritiesright. Epidemiologyisabasic scienceofmedicinewhichaddresseskeyquestionssuchas"Whobecomesill?"and "Whatareimportantprognosticfactors?" Answerstosuchquestionsprovidethe basisforbetterpreventionandtreatmentofdiseases. Many people contributed to the writing of this book: medical students in Denmark,studentsofepidemiologyattheIEAEEPEsummercourseinFlorence, Italy,andstudentsofpublichealthinLosAngeles. Withouttechnicalassistance v vi Preface fromGitteNielsen,JenadeShelley,NinaHoheandPamMasangkaythebookwould neverhavematerialized. LosAngeles,California JornOlsen Odense,Denmark KaareChristensen IowaCity,Iowa JeffMurray Stockholm,Sweden AndersEkbom Contents Part I Descriptive Epidemiology 1 Measures of Disease Occurrence ...3 IncidenceandPrevalence ...4 Incidence...6 RatesandDynamicPopulations ...7 CalculatingObservationTime...9 Prevalence,Incidence,Duration ...10 MortalityandLifeExpectancy ...11 LifeExpectancy ...12 References...13 2 Estimates of Associations ...15 3 Age Standardization...19 4 Causes of Diseases ...23 References...28 5 Descriptive Epidemiology in Public Health...29 GraphicalModelsofCausalLinks ...33 References...35 6 Descriptive Epidemiology in Genetic Epidemiology...37 OccurrenceDatainGeneticEpidemiology ...37 ClusteringofTraitsandDiseasesinFamilies ...38 TheOccurrenceofGeneticDiseases ...40 References...41 7 Descriptive Epidemiology in Clinical Epidemiology...43 SuddenInfantDeathSyndrome(SIDS)...44 CytologicalScreeningforCervixCancer ...45 ChangesinTreatmentofJuvenileDiabetes ...46 References...47 vii viii Contents Part II Analytical Epidemiology 8 Design Options...51 CommonDesignsUsedtoEstimateAssociations...51 EcologicalStudy ...52 Case-ControlStudy...54 CohortStudy ...5 5 ExperimentalStudy ...56 Reference ...57 9 Follow-Up Studies ...59 TheNon-experimentalFollow-Up(Cohort)Study ...59 StudyingRiskasaFunctionofBMI ...60 LongitudinalExposureData...62 DifferentTypesofCohortorFollow-UpStudies...63 10 Case-Control Studies...67 Case-CohortSampling ...69 DensitySamplingofControls...69 Case-Non-caseStudy...71 PatientControls ...72 SecondaryIdenti cationoftheSourcePopulation ...74 Case-ControlStudiesUsingPrevalentCases...74 WhentoDoaCase-ControlStudy? ...77 References...78 11 The Cross-Sectional Study...79 12 The Randomized Controlled Trial (RCT) ...81 Reference ...

Examines the economic impact of aid, but not in the sense that it questions the relevance of this objective, or tries to measure whether aid works or not. The focus of this book is on the evaluation process itself. Can aid evaluation be improved in order to increase the effectiveness of aid?